A dye-sensitized solar cell generally has an electrode having an oxide semiconductor as a carrier for a dye. The dye supported on the carrier is to be excited on absorbing incident light and inject electrons into the carrier to perform photoelectric conversion. Dye-sensitized photoelectric solar cells of this type are expected to theoretically achieve high energy conversion efficiency and be produced at lower cost than those having a conventional silicone semiconductor, which will provide a great economical advantage.
The photoelectric efficiency of a solar cell is represented by the product of the generated current and the generated voltage. Approaches to the improvement of generated current under study include development of a dye having a broadened absorption wavelength range and a combined use of dyes having different absorption wavelength ranges. Organic dyes such as ruthenium complex dyes and cyanine dyes are widely known for use in dye-sensitized solar cells. Inter alia, various studies have been directed to cyanine dyes for their relatively high stability and ease of synthesis. For example, Patent Document 1 below discloses a cyanine dye having a carboxyl group as an anchor group to be adsorbed onto an oxide semiconductor electrode.
On the other hand, studies on changing an electrolyte have been reported as an approach to the improvement on generated voltage. Specifically, it has been proposed to replace an iodine-based electrolyte, which has been commonly used mainly for its low cost, with (SCN)2/SCN−, (SeCN)2/SeCN−, a cobalt-based electrolyte, and so forth as described in Non-patent Documents 1 and 2 and Patent Document 2 below. Patent Document 3 below discloses the study on dyes for use in dye-sensitized solar cells containing a cobalt-based electrolyte.